1. Technical Field
The present invention relates to a projector.
2. Related Art
Projectors are apparatuses for modulating light beams, which are emitted from light sources, based on image signals to form optical images, and projecting the optical images, thus formed, on projection object surfaces such as screens via projection lenses and so on. In the past, polarization conversion element arrays for converting light beams emitted from light sources into a single type of linearly polarized light beams have been used in projectors for the purpose of improving the efficiency of the emitted light beams. Further, a part of the light beam entering the light beam entrance surface of the polarization conversion element array is input to an effective entrance area of the polarization conversion element array as an incident light beam intended to be input. In contrast, with respect to an ineffective entrance area (i.e., an area to which the incident light beam is not intended to be input) of the polarization conversion element array, there is disposed a light shielding plate for shielding the light beam on an anterior side of the entrance surface of the polarization conversion element array, for example.
JP-A-2007-65519 (Document 1) discloses a projector video apparatus provided with a polarization conversion element having a first light shielding plate and a second light shielding plate. The first light shielding plate has a plurality of first opening sections and second opening sections arranged between the first opening sections. The plurality of first opening sections each have a shape corresponding to the entrance areas (the effective entrance areas) of the polarization conversion element and is disposed at intervals corresponding respectively to a plurality of the entrance areas arranged at predetermined intervals on the entrance surface of the polarization conversion elements. The plurality of second opening sections each have an area smaller than the entrance area arranged thereon. The first light shielding is slidably provided on the polarization conversion element. The second light shielding plate has a plurality of opening sections, which has shapes corresponding to the plurality of entrance areas, arranged at predetermined intervals. According to this apparatus, by sliding the first light shielding plate with respect to the second light shielding plate, the contrast characteristic of a video image projected on a screen with reduced light intensity is improved.
Further, in JP-A-2004-138746 (Document 2), there is disclosed the fact that a light shielding section is provided to a slit-like opening plate provided with a slit corresponding to the effective area of the polarization conversion element, and the light shielding section limits the incident angle and incident orientation of the light entering a second liquid crystal panel, thereby improving the contrast.
Further, in JP-A-11-231264 (Document 3), there is disclosed the fact that the light shielding section is formed by evaporating aluminum in the ineffective entrance area of the polarization conversion element array. According to this light shielding section, since the aluminum is directly evaporated in the ineffective entrance area, the thermal conductivity is also improved in comparison with a configuration in the related art of separately disposing the light shielding plate, thus the cooling efficiency of the polarization conversion element array can be improved.
However, if the two light shielding plates, namely the first light shielding plate and the second light shielding plate, are provided as described in the Document 1, the number of components of the light shielding plates is increased, and the sliding structure becomes complicated, which causes a problem of increasing the component cost and the assembling cost of the projection video apparatus. Further, when cooling the polarization conversion element using a cooling fan, there is a conceivable problem that the use of two light shielding plates causes the cooling air to be blocked, which degrades the efficiency of cooling the polarization conversion element. Further, since the configuration of the Document 2 is substantially the same as the related art configuration, the efficiency of cooling the polarization conversion element is also substantially the same as that in the related art. Therefore, projectors capable of improving the efficiency of cooling the polarization conversion element array, and improving the contrast of the projected images have been requested.